When the alarm bells sounded on Capitol Hill on Tuesday afternoon, Rep. G.K Butterfield was in closed door meeting with the Republican Majority Leader. The topic: gun violence.

"When the buzzer went off that we were on lockdown, the Capitol Police rushed in to our room and barricaded us into the room," Rep. Butterfield said.

Butterfield is a Wilson Democrat who represents North Carolina's 1st Congressional District.

There was unmistakable irony between the topic of Butterfield's meeting and the cause of the Capitol Hill lockdown.

For the second time in four days, the U.S. Capitol was being placed on lockdown because of reports of a gunman nearby.

Tuesday, cameras near a tunnel just south of Capitol Hill captured the takedown. D.C. Metropolitan Police arrested three men they say shot at police officers with a small machine gun.

With both the House and Senate in session, the U.S Capitol and its office buildings were locked down by police.

"We could see out the window of the Capitol from the majority leader's office and see the officers on alert," Butterfield said. "We could see the officers holding their guns and looking for these suspects."

Police said the suspects fired at officers with a Mac-11, a subcompact machine gun. No one was injured.

Officers recovered the weapon inside the tunnel after it was allegedly dropped by the suspects.

Police gave the all-clear at 4:45 p.m., about a half hour after the incident began.

"And it's just coincidental we were talking about how to curb gun violence in America," said Butterfield who used the day's scare as another example of the nation's need for tighter gun control measures.

"All of us share the responsibility of curbing violence in America and we're not going to do that until we sit down and have meaningful dialogue."

Congressman Butterfield said to expect an announcement as early as Wednesday from House Speaker Paul Ryan about a bipartisan commission tasked to study new ways to tackle gun violence in America.